Fluid-tight electric fuse

ABSTRACT

An electric fuse rendered fluid-tight by means of a single piece sleeve of a heat-shrinkable and heat-shrunk substance. The sleeve covers the cylindrical casing of the fuse and the lateral surfaces of cylindrical coaxial extensions of terminal plugs of the fuse having substantially the same diameter as the inner diameter of the casing. The portions of the sleeve overlapping the lateral surfaces of the aforementioned extensions are clamped against said surfaces by annular metal clamps which are provided with adjustment or clamping screws.

United States Patent 9;

Kozacka et al.

[ 1 Nov. 12, 1974 FLUID-TIGHT ELECTRIC FUSE Inventors: Frederick J.Kozacka, South Hampton, N.H.; Erwin Salzer, Waban, Mass.

Assignee: The Chase-Shawmut Company,

Newburyport, Mass.

Filed: Nov. 9, 1973 Appl. No.: 414,307

US. Cl. 337/246, 337/248 Int Cl. HOlh 85/14 Field of Search 337/186,205, 222, 248,

' References Cited UNITED STATES PATENTS 6/1954 Kozacka et al. 337/24611/1971 Trimble l74/D1G. 8

Harmon 1 337/248 Toth 1. 174/D1G. 8

Primary E.\'arninerR. N. Envall, Jr, Attorney, Agent, or Firm-ErwinSalzer [57] ABSTRACT An electric fuse rendered fluid-tight by means of asingle piece sleeve of a heat-shrinkable and heat-shrunk substance. Thesleeve covers the cylindrical casing of the fuse and the lateralsurfaces of cylindrical coaxial extensions of terminal plugs of the fusehaving substantially the same diameter as the inner diameter of thecasing. The portions of the sleeve overlapping the lateral surfaces ofthe aforementioned extensions are clamped against said surfaces byannular metal clamps which are provided with adjustment or clampingScrews.

5 Claims, 3 Drawing Figures 1 FLUID-TIGHT ELECTRIC FUSE BACKGROUND OFTHE INVENTION There is a long-felt need for fluid-tight fuses, and thereare a number of prior art fuses attempting to fill that need. One of themeans which is widely used to make fuses fluid-tight, e.g. to allow theinstallation thereof in damp vaults, is the provision of so-called bootsformed of two parts of an elastomeric material which overlap in themedian region of the fuse and form bushinglike extensions situated atthe ends of the fuse remote from said median region for receiving theterminals of the fuse, or outgoing lines, respectively. Such boots arerelatively expensive and the installation thereof is also relativelyexpensive. Another way of rendering electric fuses fluid-tight involvinga single unitary fluid-tightening layer is disclosed in U.S. Pat. No.2,681,398 to F. J. Kozacka, et al, June 15, 1954 for FLUID-TIGHT FUSESTRUCTURE. The cost of manufacturing fluid-tight fuses as disclosed inthe above patent is also relatively high. Instead of achievingfluidtightness'by mounting sleeve-like means on non-fluidtight fuses,fuses can be manufactured which are inherently fluid-tight and,therefore, do not call for additional sleeve-like means to achievefluid-tightness. The cost of manufacturing fuses which are inherentlyfluidtight are relatively high, and preclude the use of certainmaterials and design features which are highly desirable. Fuses whichare not fluid-tight are sometimes enclosed in fluid-tight housings forinstallation in damp locations, which greatly increases the bulk and thecost of any such installation. Non-fluid-tight fuses intended for theprotection of transformers have been installed in fluid-tight housingssubmersed in the fluid, e.g., oil,

. inside the tank of the transformer. Such arrangements are not onlyrelatively expensive and bulky, but ineffective inasmuch as the fluidinside the transformer tank is not, or is not efficiently, used forcooling of the fuses.

It will be apparent from the above that though many solutions have beenoffered to achieve fluid-tightness of fuses, all prior art solutions tothe problem under consideration are subject to limitations, anddrawbacks.

New possibilities of achieving fluid-tightness of mis- I SUMMARY OF THEINVENTION Electric fuses embodying this invention have plug terminalsclosing the cylindrical casing thereof and are enclosed in a fluid-tightsingle piece sleeve of a heatshrinkable and heat-shrunk substance understress. The plug terminals have cylindrical coaxial extensions integralwith said plug terminals projecting axially beyond the casing of thefuse to the outside of said casing. These extensions have an outerdiameter substantially equal to the inner diameter of the casing of thefuse so that the extent of shrinkage required to mount said sleevetightly on said casing and to mount said sleeve tightly on saidextensions is substantially equal. Fuses embodying this inventionfurther include annular metal clamps having adjustment screws orclamping screws for varying the extent of the periphery thereof. Theseannular metal clamps are mounted on the aforementioned extensions of theterminal plugs and on portions of said sleeve overlapping saidextensions and clamp said overlapping portions of said sleeve againstsaid extensions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a first embodyment of theinvention partly in front elevation and partly in longitudinal section;

FIG. 2 shows in the same way as FIG. 1 a modification of the structureof FIG. 1; and

FIG. 3 is a top plan view of structures of the kind shown in FIGS. 1 and2.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings,fuses of the kind illustrated therein are disclosedmore in detail inU.S. Pat. No. 3,599,138 to Frederick J. Kozacka, issued Aug. 10, 1971for HIGH-VOLTAGE FUSE. Reference may be had to that patent in regard todetails involving such fuses, but having no immediate bearing on thepresent invention.

FIGS. 1 and 2 illustrate the upper portion and the lower portion of afuse structure for elevated circuit voltages, its center portion ormedian portion being broken away, or deleted.

The fuses shown include a tubular cylindrical casing l of electricinsulating material, e.g., melamine glasscloth. The ends of casing 1 areclosed by cylindrical plug terminals 2 press-fitted into casing l andfirmly held in position by steel pins 3 projecting transversely orradially through casing 1 into plug terminals 2. Plug terminals 2 arespaced by four spacing plates 4 of electric insulating material. Theaxially outer ends of plates 4 are affixed to plug terminals 2 as, forinstance, by means of grooves provided in the axially inner end surfacesof plug terminals 2. This is shown in in detail in the above referred-t0U.S. Pat. No. 3,599,138. A fusible element 12 in form of a silver ribbonis wound heli cally around the radially outer edges of spacing plates 4.The ends of fusible element 12 are conductively connected to the axiallyinner end surfaces of plug terminals 2. This may be achieved by themeans more fully disclosed in U.S. Pat. No. 3,57l,775 to F. J. Kozacka,et al, Mar. 23, 1971 for HIGH-VOLTAGE FUSE HAVING A PLURALITY OFHELICALLY WOUND RIBBON LINKS. Casing l is filled with a pulverulentarc-quenching filler l0, e.g., quartz sand, engaging physically casing 1and the axially inner surfaces of plug terminals 2. Each plug terminal 2is provided with a coaxial extension 2a projecting axially beyondcasing 1. The outer diameter of extensions 2a is substantially equal tothe inner diameter of easing 1 so that the extent of shrinkage requiredto mount heat-shrinkable sleeve 5 tightly on casing 1 and to mount saidsleeve tightly on extensions 2a of plug terminals 2 is substantiallyequal. As shown in FIG. 1 the diameters of extenequal to the innerdiameter of casing 1. According to ery thereof. Such metal clamps areoften referred-to as hose clamps since they are widely used for clampinghoses to pipes. Clamps 6 are mounted on extensions 2a and on portions ofsleeve 5 overlapping extensions 2a and clamp said portions of sleeves 5against extensions 2a. Clamps 6 are arranged in such a way that theaxially outer edges of sleeve 5 are covered and protected by the former.This precludes tearing of sleeves 5 at their edge regions and makes itunnecessary to use wound tape generally used in like situations as, forinstance, for closing the axially outer ends of so-called boots.

The axial length of extensions 2a and the width of annular metal clamps6 are substantially equal. As a result of this configuration of parts 2aand 6, the lateralsurfaces of extensions 2a are substantially unexposed.The axial end surfaces of extensions 2a are exposed and form contactsurfaces allowing insertion of the fuse into an electric circuit bymeans of the exposed end surfaces of extensions 2a. FIGS. 1 and 3 show apair of metal straps 7 screwed by means of screws 8 against the exposedend surfaces of extensions 2a. This arrangement of parts is lessexpensive and not as bulky as connecting an electric fuse into anelectric circuit by means of ferrules which engage a fuse holder.

The particular kind of heat-shrinkable material used for achievingfluid-tightness depends very much upon the intended application. Whereresistance to mechanical action is of importance, the thickness of thesleeve 5 ought to be relatively large. This can be achieved because thedegree of required shrinkage is substantially uniform along the entirelength of sleeve 5. Mechanical strength can also be enhanced by using aheatshrinkable substance having an insert of glass-cloth. In instanceswhere mechanical ruggedness is a lesser consideration than maximizingheat transfer between the fuse and a surrounding liquid medium thethickness of sleeve 5 ought to be as small as possible.

FIG. 2 shows a fuse embodying this invention submersed in a body 9 ofcooling liquid. Sleeve 5 is shrunk so as to engage the annular planarareas A situated between the lateral surface of casing l and the lateralsurfaces of extensions 2a. Such a close fit cannot be achieved if thediameter of extensions 2a is significantly less than the diameter ofplug terminals 2.

The clamp 6 may be arranged in such a way that screw 6a may assume anydesired angular position. In

' FIG. 1 the upper clamp 6 is shown with its clamping respectiveclamping screws, these screws being sectioned away in FIG. 2. FIG. 3 hasbeen drawn assuming that both the upper clamp 6 and the lower clamp 6and their respective clamping screws 6a are arranged in registry.

We claim as our invention:

1. An electric fuse including a cylindrical casing of electricinsulating material, a pulverulent arcquenching filler inside of and inengagement with said casing, metallic plug terminals having an outerdiameter equal to the inner diameter of said casing plugging the ends ofsaid casing, fusible element means inside said casing immersed in saidpulverulent arc-quenching filler conductively interconnecting said pairof plug terminals and a fluid-tight single piece sleeve ofheatshrinkable and heat-shrunk substance mounted under stress upon saidcasing wherein the improvement comprises a. cylindrical coaxialextensions on and integral with said plug terminals projecting axiallybeyond said casing to the outside of said casing, said extensions havingan outer diameter substantially equal to the inner diameter of saidcasing so that the extent of shrinkage required to mount said sleevetightly on said casing and to mount said sleeve tightly on saidextensions is substantially equal; and annular metal clamps havingadjustment screws for varying the extent of the periphery thereofmounted on said extensions and on portions of said sleeve'extendingbeyond said casing and overlapping said extensions, said annular metalclamps clamping said portions of said sleeve against said extensions.

2. An electric fuse as specified in claim 1 wherein the diameter of saidextensions is equal to the inner diameter of said casing so that saidplug terminals and said extensions thereof have lateral surfaces whichare a continuous cylindrical surface.

3. An electric fuse as specified in claim 1 wherein the axially outeredges of said sleeve are covered and protected by said annular metalclamps.

4. An electric fuse as specified in claim 1 wherein the axial length ofeach of said extensions and the width of each of said annular metalclamps are substantially equal so that the lateral surfaces of saidextensions are substantially unexposed and wherein the axial endsurfaces of said extensions are exposed and form contact surfacesallowing insertion of said fuse into an electric circuit by means ofsaid exposed end surfaces of said extensions.

5. An electric fuse as specified in claim 1 being submersed in a body ofliquid and having a sleeve shrunk so as to engage tightly the planarannular areas situated between the lateral surface of said casing andthe lateral surfaces of said extensions.

1. An electric fuse including a cylindrical casing of electricinsulating material, a pulverulent arc-quenching filler inside of and inengagement with said casing, metallic plug terminals having an outerdiameter equal to the inner diameter of said casing plugging the ends ofsaid casing, fusible element means inside said casing immersed in saidpulverulent arcquenching filler conductively interconnecting said pairof plug terminals and a fluid-tight single piece sleeve ofheat-shrinkable and heat-shrunk substance mounted under stress upon saidcasing wherein the improvement comprises a. cylindrical coaxialextensions on and integral with said plug terminals projecting axiallybeyond said casing to the outside of said casing, said extensions havingan outer diameter substantially equal to the inner diameter of saidcasing so that the extent of shrinkage required to mount said sleevetightly on said casing and to mount said sleeve tightly on saidextensions is substantially equal; and b. annular metal clamps havingadjustment screws for varying the extent of the periphery thereofmounted on said extensions and on portions of said sleeve extendingbeyond said casing and overlapping said extensions, said annular metalclamps clamping said portions of said sleeve against said extensions. 2.An electric fuse as specified in claim 1 wherein the diameter of saidextensions is equal to the inner diameter of said casing so that saidplug terminals and said extensions thereof have lateral surfaces whichare a continuous cylindrical surface.
 3. An electric fuse as specifiedin claim 1 wherein the axially outer edges of said sleeve are coveredand protected by said annular metal clamps.
 4. An electric fuse asspecified in claim 1 wherein the axial length of each of said extensionsand the width of each of said annular metal clamps are substantiallyequal so that the lateral surfaces of said extensions are substantiallyunexposed and wherein the axial end surfaces of said extensions areexposed and form contact surfaces allowing insertion of said fuse intoan electric circuit by means of said exposed end surfaces of saidextensions.
 5. An electric fuse as specified in claim 1 being submersedin a body of liquid and having a sleeve shrunk so as to engage tightlythe planar annular areas situated between the lateral surface of saidcasing and the lateral surfaces of said extensions.